Electrochemical Transducer Array and Use Thereof

ABSTRACT

Electrochemical transducer arrays are already known from the prior art. According to the invention, the transducer array is provided with at least one flexible, planar metal substrate on which at least one flexible insulator having a firm connection between the metal surface and the insulator surface is disposed. The metal substrate and the insulator disposed thereon are structured in such a manner as to give metal areas which are electrically insulated the one from the other and which serve as sensor areas. The metal substrate used is self-contained so that the structured metal areas can be contacted from the lower side.

This application is the national phase under 35 U.S.C. § 371 of PCTInternational Application No. PCT/EP2005/050332 which has anInternational filing date of Jan. 26, 2005, which designated the UnitedStates of America and which claims priority on German Patent Applicationnumber 10 2004 004 653.0 filed Jan. 29, 2004, the entire contents ofwhich are hereby incorporated herein by reference.

FIELD

The invention generally relates to an electrochemical transducer array,and/or to specific uses of a transducer array.

BACKGROUND

Electrochemical transducers are generally subdivided into the threegroups of potentiometric, conductometric and amperometric. In the caseof potentiometric transducers, the potential is measured with respect toa reference electrode. Ion-selective sensors operate on this basis, andthe electrode is in this case coated with an ion-selective membrane. Thepotential on the electrode is then a measure of the concentration of thecorresponding ions. A potentiometric pCO₂ sensor can thus also beproduced by way of a gas-permeable membrane.

In the case of amperometric transducers, in contrast, a voltagedifference is produced between two electrodes, in the case of which thesubstance to be detected is converted. The currents which flow duringthe reduction or oxidation process result in the measurement signal.These are widely used as oxygen sensors or biochemical sensors. In thecase of a Clark-analogous oxygen sensor, a gas-permeable membrane isapplied to the amperometric sensor.

In the case of biochemical sensors, molecular identification systems,such as haptens, antigens or antibodies are placed on or in the vicinityof the electrodes. The target molecule binds thereto and is providedeither directly or via intermediate steps with an enzyme label. If thecorresponding enzyme substrate is now added, the enzyme releases asubstance which can be detected. This is done either optically orelectrochemically. This is the so-called ELISA test (Enzyme LinkedImmuno Sorbent Assay). DNA analysis methods can also be carried out in asimilar way.

The transducers which are used for electrochemical detection mustinclude electrodes with which electrical contact is made individually.During use of potentiometric transducers, the resultant equilibriumpotential with respect to a reference electrode must be able to bemeasured. In the case of amperometric and conductometric transducers, itmust be possible to potentiostat the electrodes, and it must be possibleto detect the current flow through the electrodes individually.

One example of planar ion-selective sensors is described in E. Jacobs etal, “Analytical Evaluation of i-STAT Portable Clinical Analyzer and Useby Nonlaboratory Health-Care Professionals”, Clinical Chemistry, 39,1069 et seq. (1993). This is a silicon substrate with thin-filmelectrodes and ion-selective membranes. The sensor electrodes andcontacts are in this case located on the same side of the siliconsubstrate. In order thus to separate the contact surfaces and the flowcell for the analyte, the substrate must be considerably larger than thearea which is actually required by the sensors.

Various biochips are likewise manufactured using silicon technology, andare described R. Thewes et al, “Sensor Arrays for Fully Electronic DNADetection on CMOS”, ISSCC Digest of Tech. Papers, 2002, 350 et seq. Thishas the advantage of the integration of CMOS circuit technology, signalprocessing (multiplexing) and analog/digital conversion in the sensorplatform itself. A large number of sensors can thus be provided in avery small area. One disadvantage relates to the costs for production ofa chip such as this and the complex handling (contact-making). The costsper individual sensor are thus high for so-called low-density arrayswith fewer than 100 sensors per square centimeter.

Theoretically, it is possible to use polymer mounts with electrodesfitted to the polymer mounts, as an alternative. These can bevapor-deposited or printed on. This method makes it possible to produceindividual sensors, for example glucose sensors, at low cost[WO2002/02796-A2]. However, it is not very suitable for arrays since theconductor track structures are coarse, so that the number of electricalcontacts is greatly restricted.

Printed circuit board technology is used in the already known eSensor™from the Motorola Company in order to produce a “low-density” DNAdetection system. In this case, both the sensor surfaces and theconductor tracks and contacts are formed on the metallization layer. Theproduct is a rigid printed circuit board with sensors and contacts onthe same side. Rear-face contacts can be provided by through-plating.This technique can, however, be implemented only at high cost forlarge-scale manufacture.

Furthermore, by way of example, so-called microelectrode arrays areknown from EP 0 504 196 B1 and DE 197 17 809 U1, in which the sensorcavities have as small an area as possible. DE 199 16 921 A1 discloses amethod for production of arrays which are arranged in pairs and arecomposed of microelectrodes, in which the mount is either silicon orplastic. The aim in this case is to be able to drive the individualelectrodes separately. DNA analysis is quoted in particular as anapplication.

Finally, WO 2004/001404 A1 discloses an array of microelectrodes inwhich the structure can be varied. The array mounts are in this caseglass and/or Captan films, with a single reference-ground electrodebeing used. Finally, DE 199 29 264 A1 discloses a universal transducerfor chemosensors and biosensors, in which a multilayer system isprovided with isolating layers and electrode layers, which are used asworking, reference-ground and counterelectrodes. The large number ofknown transducer arrays therefore place particular emphasis on specificmicroelectrodes, with contact always being made from above.

SUMMARY

In at least one embodiment of the invention, a suitable transducer arrayis provided which is simple to handle and can be produced at low cost.In at least one additional embodiment, uses of the transducer array areprovided.

In the transducer array according to at least one embodiment of theinvention, at least one flexible, planar metal substrate is provided, onwhich at least one flexible isolator is arranged with a permanentconnection between the metal surface and the isolator surface. In thiscase, both the self-supporting metal substrate and the isolator arestructured in such a manner that metal surfaces are formed which areelectrically isolated from one another and provide the sensor surfaces,in which case the structured metal areas of the self-supporting metalsubstrate can be contacted from the side facing away from the sensorsurface or the side opposite the sensor. This results in a simplemeasurement capability by way of needle contacts, particularly fordecentralized measurement by way of smart cards.

One particularly advantageous feature of at least one embodiment of theinvention is the good handling capability of the product. The product isa material composite which is only 100 μm to 200 μm thick and can occupyany desired area. The sensor array is thus highly flexible and, with anappropriate geometry, can be guided on rollers. In the simplest case,the composite comprises a metal layer and an isolator layer. The frontface of the metal substrate is covered by the isolator, with only smallmetal surfaces remaining, which represent the sensors.

Generally, the sensors have to be resistant to aqueous electrolytes andalso have to have catalytic activity for the conversion of the chemicalsubstance to be detected. In order to achieve this, they can be coatedwith noble metals such as platinum, gold or silver. Depending on therequirements of the circuit technology, some areas can be in the form ofreference electrodes or counterelectrodes. In particular, it is possibleto use a sensor surface coated with silver and chlorided as a referenceelectrode.

The metal layer can advantageously be used on both sides. The sensorsare located, as described, on the front face. The rear face is used tomake contact with the sensors. In this case, the metal layer isstructured such that each sensor is electrically isolated from theothers. The rear-face metal surface which this results in and whichcorresponds to a single sensor on the front face is considerably largerthan the sensor surface. Contact can thus be made at a point which isnot located directly underneath a sensor surface and is reinforced bythe isolator. Since the metal substrate is self-supporting, therear-face contact may, however, also be made directly underneath thesensor surface in order in this way to allow a particularly space-savingembodiment. One proposed way to make contact is to use needle cards,which are also used in the application examples.

In the case of a very large sensor array in the form of a strip, it ispossible not to make contact with all of the sensors at the same time,but to move in the form of a magazine through the measurement apparatus.The needles would automatically make contact with the sensor surfaces atthat time, with the array element being available as an “endless array”for the measurements. This procedure is particularly important for usefor automatic monitoring of processes.

Titer plates play an important role in analysis (for example HTS: HighThroughput Screening). These contain 96 (8*12), 384 (16*24) or 1536(32*48) small plastic reaction pots with grid sizes of 9 mm, 4.5 mm and2.25 mm, respectively. In some cases, optical detection processes can becarried out directly using titer plates such as these. For this purpose,the titer plates have, for example, planar, optically transparent bases.The transducer arrays according to the invention can in this caseadvantageously be used for electrochemical detection. For this purpose,they are matched to the external dimensions of the titer plates and tothe grid side of the small reaction pots. They form the base of thetiter plates, so that each small reaction pot has at least oneassociated electrode. Since contact can be made with the rear face ofthe transducer arrays according to at least one embodiment of theinvention, contact can be made at the same time with all of theelectrodes on the titer plate, and they can thus be read at the sametime.

A further advantage of the transducer array according to at least oneembodiment of the invention, particularly in comparison to silicon-chiptechnology, is the structure of the array surface. This is not flat.Instead of this, each sensor is located in a depression, which ispredetermined by the thickness of the isolator used. These cavities areparticularly suitable for accommodation of coatings. They may containthe traps that have been mentioned for DNA analysis, antibodies orselective membranes.

In one specific embodiment, the cavity may even represent a closedelectrochemical system. At least one second electrode is required percavity for this purpose. This can be formed either by division of thesensor surface or by the introduction of a further electrode, which isplaced over the cavity as a cover. In this case, this cover is not afixed component of the sensor array, since the analyte must first beintroduced into the cavity. By way of example, it may likewise be joinedto the sensor array as a strip. The advantage of a closed arrangementsuch as this is that the substance to be detected is enclosed in thecavity. It can neither diffuse away, thus attenuating the signal, norcan it reach another sensor where it would result in an incorrectsignal.

BRIEF DESCRIPTION OF THE DRAWINGS

Further details and advantages of the invention will become evident fromthe following description of the figures of example embodiments, on thebasis of the drawings in conjunction with the patent claims.

In the figures, in each case illustrated in a schematic simplified form:

FIG. 1 and Figure show the front face and rear face of a transducerarray,

FIG. 3 shows a section illustration of a transducer array as shown inFIGS. 1/2,

FIG. 4 shows a plan view of a two-dimensional array,

FIG. 5 shows a section illustration, as a partial detail of thetransducer array shown in FIG. 4 with the associated contact,

FIGS. 6 to 14 show section illustrations of various variants of atransducer array as shown in FIGS. 1/2,

FIG. 15 shows a measurement apparatus using a transducer array as shownin FIGS. 3 to 14,

FIG. 16 shows the results of use of a transducer array as anion-selective sensor, and

FIG. 17 shows results of the use of a transducer array corresponding toone of FIGS. 1 to 14 as a DNA sensor.

DETAILED DESCRIPTION OF THE EXAMPLE EMBODIMENTS

FIGS. 1 and 2 show the front and rear faces of a sensor array comprisinga metal substrate 1 and an isolator layer 2. By way of example, circulardepressions 3 _(i), which are referred to as cavities, are illustratedon the front face. The cavities 3 _(i) are produced by the structuringof the isolator 2. The surface of the metal substrate at the bottom ofthe depressions 3 _(i) is exposed.

The illustration of the rear face uses oblique lines to show thesubdivision of the metal substrate 1 into parts 10 _(i) which areisolated from one another. Each metal island 10 _(i) corresponds to thecavity 3 _(i) of an isolator cutout on the front face. The possiblecontact points for a so-called needle card for selectively makingelectrical contact with the metal surfaces are indicated by dots on therear face.

FIG. 3 shows a side view of a sensor array, in the form of a sectionthrough one row of electrodes or sensors. The separating lines in themetal substrate 1 are illustrated as singular measurement electrodes 10_(i) with a measurement area 12 _(i) and an opposite face as acontact-making surface 11 _(i). The isolator 2 is located above this, iscomposed of individual elements 20 _(i), holds the self-supporting metalsurfaces together, and isolates them from one another.

FIG. 4 shows a plan view of a two-dimensional m×n sensor array, in whichthe cavities 3 _(i) and the measurement surfaces 12 _(i) are locatedclose to one another. The adjacent cavities 3 _(i) and 3 _(i+1) withmeasurement surfaces are indicated in the array, in which case the aimis to be able to make contact with the array on the side 11 _(i) facingaway from or opposite the sensor surface 12 _(i). While one sensor isdirectly adjacent to the other sensors in the area of the m×n array, aside metal area remains free on the rear face of the outer sensor row,for making contact with.

FIG. 5 shows a detail of the sensor array from FIG. 4 with electrodesfitted from the lower face of the metal substrate 1 in order to tap offmeasurement signals. The measurement technique with the associatedmeasurement apparatus and the electrode arrangement that isadvantageously used in this case will be described in detail furtherbelow with reference to FIG. 10.

In the case of the first sensor surface, one contact 4 a is fitted tothe metal surface 11 _(i), which is exposed on both sides, centrally,directly opposite the sensor surface. In contrast, in the case of thesecond sensor surface, contacts 4 b may be fitted to the metal surface,which is exposed on one side, laterally offset with respect to thesensor surfaces, since there is sufficient remaining space here.

FIG. 6 shows a sensor array with two electrodes per cavity. For thispurpose, the metal substrate is split at this point. The resultant gapis closed by an additional isolator layer 40 _(i) from the lower face.In this case, contact surfaces remain free and define measurementelectrodes. A working electrode WE and a counterelectrode CE areintroduced alternately.

FIG. 7 shows that a plurality of cavities are wetted by the sameelectrolyte. The metal surface of one cavity can then be polarized inthe opposite direction to the metal surface of another cavity.

FIG. 8 shows that one of the open metal surfaces is covered on the frontface by a thin silver/silver chloride layer. This layer 40 ₁ can beconnected to a potentiostat, together with two further wetted metalsurfaces, in a three-electrode arrangement as a working electrode (WE),a counterelectrode (CE) and a reference electrode (Ref).

FIG. 9 shows the use of an external reference electrode 15, which isimmersed in the common electrolyte which also wets at least two metalsurfaces. Together, they can be connected to a potentiostat in athree-electrode arrangement.

FIG. 10 shows an external reference electrode which is immersed in thesame electrolyte as that which also wets a plurality of cavities, eachhaving two electrodes. The two electrodes together with the referenceelectrode in each case form a three-electrode arrangement.

FIG. 11 shows that the electrolyte areas in each cavity can beelectrically isolated from the other electrolyte areas.

FIG. 12 shows that an electrical conductor which is located above thecavities can be used as a common counterelectrode CE for all of thecavities. A voltage is in each case applied between the metal surface inthe cavity and the common counterelectrode.

FIG. 13 shows that, in the case of a sensor array with two electrodesper cavity 3 _(i) and 3 _(i), one of the two electrodes is coated withsilver/silver chloride (Ag/AgCl). This coated electrode is connected asa reference electrode to a potentiostat, together with the secondelectrode in the cavity as the working electrode, and the coveringcounterelectrode, in a three-electrode arrangement.

FIG. 14 shows that an electrode which covers the measurement arrangementis coated with silver/silver chloride on the electrolyte side. Thesensor array has two electrodes per cavity. A three-electrodearrangement can thus be produced with these two electrodes as theworking electrode WE and the counterelectrode CE, and with the coveringelectrode as the reference electrode.

FIG. 15 illustrates the measurement apparatus in detail. In this case,use can be made of the method of “pulsed” redox cycling, which isdescribed in detail in a parallel application from the same applicant,with the same application priority, and entitled “Method for measurementof the concentration or concentrate change of a redox-active substance,and an associated apparatus”.

Apart from being formed by a transducer array 100, various variants ofwhich have been described on the basis of the FIGS. 3 to 14, themeasurement layout is essentially provided by a suitable potentiostat 5in combination with a pulse generator 6, which optionally producessquare-wave, triangular-waveform or sinusoidal pulses. The potentiostat5 is designed in such a manner that suitable potentials are produced, bymeans of two operational amplifiers 7 and 7′, one of which is connectedto a “ground” potential, and to one defined measurement resistance. Inthis case, the pulse duration, the repetition rate and the magnitude ofthe potential can be predetermined. In particular, the pulse durationsof the measurement phases and the relaxation phases can be adjustedseparately, and may be of different duration. The potentials may also beof different magnitudes.

The transducer array 100 is associated with the individual electrodeswhich, by definition, provide a reference electrode RE, acounterelectrode CE and at least one working electrode WE. Theseelectrodes are connected to the potentiostat 5 as a three-electrodearrangement. The signal from the potentiostat 5 is connected to a signalprocessing unit, which is not illustrated in detail in FIG. 9 but bywhich an evaluation process is carried out, taking into account theabove statements relating to the measurement method and accuracy. Ingeneral, this results in U_(out)˜I for evaluation of the signal profileillustrated in FIG. 15.

In one specific development, a transducer array corresponding to one ofthe examples described above is used as an ion-selective sensor: asensor array comprising a metal layer and an isolator layer is used forthis example application. The diameter of the cavities is 0.8 mm, thedepth is 90 μm, and the distance between two adjacent electrodes is 1mm. The electrode surfaces are covered with a 2.3 μm thick gold layer.Overall, the array comprises four electrodes, one of which is in theform of a silver chloride reference electrode. The other threeelectrodes have been coated with an ion-selective membrane. Anammonium-selective membrane is quoted as one example here.

Corresponding to the recommendation of Fluka, the membrane compositionwas:

-   -   1.00% by weight Ammonium Ionophore I (Fluka 09877)    -   33.00% by weight Poly(vinyl chloride) high molecular weight        (Fluka 81392)    -   66.00% by weight Dibutyl sebacate (Fluka 84838)

A total of 100 mg of the reagents was dissolved in 550 μl of a mixtureof cyclohexan and THF, in the ratio 8:2. In each case 35 nl, 45 nl and60 nl of this solution were spotted into the three sensor cavities, thusresulting in three membranes of different thickness. These were driedfor several hours in air.

The sensor array was inserted into a 100 μm deep through-flow channel,and solutions of different NH₄NO₃ concentrations were then pumped overit. The solutions also included 100 mM ofTris(hydroxymethyl)aminomethane/hydrochloric acid for buffering at pH 8.The potential difference between the membrane-coated electrodes and thereference-ground electrode was then measured using a high-impedanceohmmeter. The following figure shows the potential change on the sensoras a function of the NH₄ ⁺ concentration for the three membranethicknesses.

FIG. 16 shows the relationship between the potential and the acidconcentration. The concentration of NH₄NO₃ is plotted on the abscissa inmol/l, and the electrochemical potential φ with respect to an Ag/AgClelectrode is plotted on the ordinate. The graphs 161 to 164 showcharacteristics for different membranes.

The gradients of the regression lines are 54 mV, 52 mV and 48 mV fromthe thinnest to the thickest membrane. These values are somewhat lessthan the theoretical value of 59 mV at room temperature.

In another development, a transducer array corresponding to one of theexamples described with reference to FIGS. 3 to 14 is used as a DNAsensor:

The sensor array that is used corresponds to the arrangement that hasalready been described in the previous example, with four electrodesurfaces being used. One of the electrode surfaces is in the form of areference electrode Ref, another is used as a counterelectrode CE, andthe two other electrode surfaces are used as measurement electrodes orso-called working electrodes WE. On one of the working electrodes, asynthetic oligonucleotide sequence of length 25 is anchored on the goldsurface by means of a terminal thiol group. The second measurementelectrode remains free.

Both surfaces were incubated with a solution of 1 mg of bovine serumalbumin per milliliter for 15 minutes, and the sensor array was theninserted into a 100 μm deep through-flow channel. First of all, 10 μl ofa 10 μM biotinilated target sequence are pumped over the electrodeswithin about 5 minutes. After a washing step, a solution ofstreptavidin-labeled alkaline phosphatase is then passed over it. Thewashing is carried out using a buffer solution of 100 mMtris(hydroxymethyl)aminomethane titrated to pH 8 with hydrochloric acid,130 mM NaCl. After washing again, a 2 mM solution of the enzymesubstrate paraminophenyl phosphate (pAPP) in the buffer solution ispumped over the sensor array. In the presence of the enzyme alkalinephosphatase, the enzyme substrate pAPP is converted to paraminophenyl(pAP). The pAP is oxidized, with an appropriate potential on theelectrode, to form quinonimine. This process can also be reversed, withthe quinonimine being reduced to pAP again. In this case:

The reference electrode, counterelectrode and in each case one of thetwo measurement electrodes are located in a three-electrode arrangementconnected to a potentiostat. Owing to the large electrode areas, apotentiostatic measurement method would lead to major depletion of thepAP. A suitable pulsed process is therefore used.

At the start of the measurement, the positive sample, that is to say theelectrode with the trap sequence, is connected. The solution with theenzyme substrate first of all flows over the negative sample, then overthe positive sample. The flowing movement flushes pAP formed from theenzyme away from the electrodes, so that the current is constant and lowwhen the pump is switched on. If the pump is now stopped, the pAPconcentration rises with time because of the enzyme activity. This isevident in the measurement by a major rise in the current signal at 20nA/s. If the pump is switched on again, then the signal falls to theoriginal value again. This process can be repeated as often as desired.

FIG. 17 shows the profile of the measurement current with the pump“on”/“stop” at the sensor with a positive and negative sample. The graphshows the time t in s on the abscissa, and the current I in nA on theordinate. The graph 171 shows the measurement current in the profileduring an experimental investigation.

The negative sample was switched over at t=400 s. Here, the currentfirst of all falls when the pump is stopped, then remains constant for ashort time, and then rises slowly. This rise is caused by the diffusionof pAP from the positive sample to the negative sample. When the pump ison, a peak current is added, since the electrolyte first of all flowsfrom the positive sample to the negative sample, and thus transports anincreased pAP concentration to the adjacent electrode. Overall, thisresults in very good discrimination of the positive and negative sample.

Example embodiments being thus described, it will be obvious that thesame may be varied in many ways. Such variations are not to be regardedas a departure from the spirit and scope of the present invention, andall such modifications as would be obvious to one skilled in the art areintended to be included within the scope of the following claims.

1. A biosensor operating on an electrochemical detection principle,comprising: a transducer array, containing a flexible metal/isolatorcomposite composed of a metal layer and an isolator layer with apermanent connection between the metal surface and the isolator surface,the metal layer being in the form of a self-supporting metal substrateand being structured in such a manner that metal areas which areelectrically isolated from one another are produced, the isolator,located on the metal substrate, being structured in such a manner thatopen metal surfaces remain as sensor surfaces in the isolator surface,wherein, the structured metal areas are contactable with, on a sidefacing away from or opposite the sensor surface, discrete electrodes,the individual metal areas each including associated individualmeasurement electrodes on the one hand and at least one referenceelectrode on the other hand.
 2. The electrochemical biosensor as claimedin claim 1, wherein the isolator layer forms cavities over the sensorsurfaces.
 3. The electrochemical biosensor as claimed in claim 1,wherein electrical contacts are provided, with the contacts and thesensor surfaces being located on opposite sides of the metal/isolatorcomposite.
 4. The electrochemical biosensor as claimed in claim 3,wherein the contacts are fitted to the metal areas, which are exposed onboth sides, directly opposite the sensor surfaces.
 5. Theelectrochemical biosensor as claimed in claim 3, wherein the contactsare fitted to the metal areas, which are exposed on one side, such thatthey are laterally offset with respect to the sensor surfaces.
 6. Theelectrochemical biosensor as claimed in claim 1, wherein a single sensorsurface contains at least two electrically isolated metal areas.
 7. Theelectrochemical biosensor as claimed in claim 6, wherein gaps which formadditional isolator areas are formed between the two metal areas on thecontact side.
 8. The electrochemical biosensor as claimed in claim 7,wherein the additional isolator areas leave metal areas free forelectrical contact to be made.
 9. The electrochemical biosensor asclaimed in claim 1, wherein the sensor surfaces are composed of a noblemetal or a noble metal alloy.
 10. The electrochemical biosensor asclaimed in claim 1, wherein the sensor surfaces are coated with a noblemetal or a noble metal alloy.
 11. The electrochemical biosensor asclaimed in claim 1, wherein electrodes are provided on a graphite base.12. The electrochemical biosensor as claimed in claim 1, wherein atleast one of the sensor surfaces is coated with silver/silver chloride.13. The electrochemical biosensor as claimed in claim 1, wherein anelectrolyte is provided and wets a plurality of sensor surfaces.
 14. Theelectrochemical biosensor as claimed in claim 1, wherein at least twosensor surfaces have voltage appliable to them.
 15. The electrochemicalbiosensor as claimed in claim 1, wherein at least two sensor surfaces,and one sensor surface coated with silver chloride, are connectable as athree-electrode arrangement to a potentiostat, with the sensor surfacecoated with silver chloride being the reference electrode.
 16. Theelectrochemical biosensor as claimed in claim 1, wherein a separatereference electrode is provided, and is immersed in an electrolyte. 17.The electrochemical biosensor as claimed in claim 16, wherein at leasttwo sensor surfaces and the separate reference electrode are connectableto a potentiostat.
 18. The electrochemical biosensor as claimed in claim16, wherein the electrically isolated metal areas with sensor surfaceshave voltage appliable to them.
 19. The electrochemical biosensor asclaimed in claim 16, wherein the electrically isolated metal areas ofone sensor surface and the reference electrode are connectable as athree-electrode arrangement to a potentiostat.
 20. The electrochemicalbiosensor as claimed in claim 1, wherein the cavities containbiochemical identification layers.
 21. The electrochemical biosensor asclaimed in claim 1, wherein the electrolyte areas in individual cavitiesare isolated from one another.
 22. The electrochemical biosensor asclaimed in claim 21, wherein a separate metal surface closes thecavities.
 23. The electrochemical biosensor as claimed in claim 1,wherein the sensor surfaces have a voltage appliable to them withrespect to the additional metal surface.
 24. The electrochemicalbiosensor as claimed in claim 1, wherein one additional sensor surfaceis provided per cavity and is used as a reference electrode.
 25. Theelectrochemical biosensor as claimed in claim 1, wherein the metalsurface which closes the cavities is coated with silver chloride and isused as a reference electrode.
 26. The electrochemical biosensor asclaimed in claim 1, wherein the sensor surfaces have high catalyticactivity.
 27. (canceled)
 28. (canceled)
 29. The electrochemicalbiosensor as claimed in claim 1, wherein electrodes are provided on agraphite base, in the form of a carbon paste electrode.